Glow discharge display device including an insulating envelope block with an array of cavities therein

ABSTRACT

An electrical glow-discharge matrix display tube comprises an array of cavities provided in a face of a block of electrically insulating material. A glow-discharge cathode is provided at the bottom of each cavity and an anode or anodes are provided facing the open end of each cavity so as to define an array of individually addressable glow-discharge paths. The open end of each cavity is completely surrounded by an individual recess so as to reduce the electrical leakage which would otherwise occur between adjacent cavities due to sputtered material being deposited on the face of the block. The cathodes may all be electrically separated and may cooperate with a common anode, or rows of cathodes may be interconnected and cooperate with a series of strip-shaped anodes orthogonal to the cathode rows.

United States Patent 9 [151 3,699,377 Hall et a1. 1451 Oct. 17, 1972 [54] GLOW DISCHARGE DISPLAY DEVICE 3,582,979 6/1971 Kupsky ..313/210 INCLUDING AN INSULATING 3,465,194 9/1969 Hall ..313/210 X ENVELOPE BLOCK WITH AN ARRAY g lfy X 0 CAVITIES THEREIN c agen 9 R 2,858,480 10/1958 Shadowitz ..315/169 TV [72] Inventors: Raymond Frederick Hall, Crawley;

Douglas Raymond Mainard, Primary Examiner-Palri1er c. DeMeo folds, both of England Attorney-Frank R. Trifari [73] Assignee: U.S. Philips Corporation I ABSTRACT. [22] Flled' 1970 An electrical glow-discharge matrix display tube com- [21] Appl. No.: 101,548 prises an array of cavities provided in a face of a block of electrically insulating material. A glow-discharge cathode is provided at the bottom of each cavity and [30] Fore'gn Apphcamn Pnomy Data an anode or anodes are provided facing the open end Dec. 30, 1969 Great Britain ..63,248/69 of each cavity so as to define an array of individually addressable glow-discharge paths. The open end of 52 US. Cl. ..313/204, 313/210, 313/220, each cavity s .completely surrounded by an individual 5 1 v recess so as to reduce the electrical leakage which 51 lm. c1 ..H0lj 61/10, H0 lj 61/30 would Otherwise Occur beiween adjacent cavities due [58] Field of 313/1095 210 to sputtered material being deposited on the face of 313/220 6 the block. The cathodes may all be electrically separated and may cooperate with a common anode, [56] References Cited or rows of cathodes may be interconnected and V cooperate with a series of strip-shaped anodes UNITED STATES PATENTS orthogonal to the cathode rows.

3,334,269 8/1967 LHeureux ..315/169 TV 3 Claims, 4 Drawing Figures eeeeeee- UUUUUUUUUUU P'A'TENTEDflm'msn 3.699.377

SHEETIUFZ FIC5.1.

INVENTORS BY RAYMOND F, HALL DOUGLAS R.v M INARD AGENT GLOW DISCHARGE DISPLAY DEVICE INCLUDING AN INSULATING ENVELOPE BLOCK WITH AN ARRAY OF CAVITIES THEREIN THIS INVENTION relates to an electrical glowdischarge display device comprising a block of electrically insulating material in a face of which is provided an array of cavities at the bottom of each of which is situated a glow-discharge cathode, and an anode or anodes facing the open ends of said cavities for cooperating with said cathodes to define an array of individually addressable glow-discharge paths through a gas atmosphere contained in said device, a gap containing said atmosphere being present between said open ends and the anode or anodes.

One device of this type is disclosed in copending application Ser. No. 108,965, assigned to the same assignee. If the array is a X 7 rectangular array, addressing selected glow-discharge paths either simultaneously or sequentially can cause the device to display any of the numerals 0 9.

As is well-known, electrical glow-discharges are liable to cause sputtering of the cathode material, and some sputtered material as even been found to be ejected from the cavities in a device constructed as described in the aforesaid Patent Application. Some of the sputtered material has been found to lodge on the face of the block in which the cavities are provided, and this can eventually provide an electrically conductive path from the wall of a given cavity to the walls of adjacent cavities, with the result that, when a given discharge path is addressed, adjacent paths may also be energized thereby.

It is an object of the invention to provide a solution to this problem.

The invention provides an electrical glow-discharge display device comprising a block of electrically insulatin g material in a face of which is provided an array of cavities at the bottom of each of which is situated a glow-discharge cathode, and an anode or anodes facing the open ends of said cavities for co-operating with said cathodes to define an array of individually addressable glow-discharge paths through a gas atmosphere contained in said device, a gap containing said atmosphere being present between said open ends and the anode or anodes, the open end of each cavity being completely surrounded by a recess provided in said face, which recess extends between the open end of the cor responding cavity and the open end of each other said cavity.

The provision of such recesses can substantially prevent sputtered material from forming a conductive path between said cavity wall and adjacent ones.

It has been found to be convenient to manufacture such devices by molding the block around an array of cathodes. Posts must then be provided in the surface of the mold corresponding to said block face in order to provide the cavities, and this is easily done by cutting an orthogonal network of grooves in the mould surface. However, if the recesses in the block face are to be created by closed ridges in the mould surface these are not so easily provided, and it has been found preferable to generate the recesses in the block face by providing closed ridges surrounding each cavity. The mould surface must then be provided with a closed groove surrounding each post, and this may be done for each groove by rotation about axis XX of a specially shaped cutter which forms the corresponding post at the same time. Thus, in a device according to the invention, said recesses may be generated by the provision of separate ridges on said block face, said ridges completely surrounding the open end of each cavity, the recesses thus formed extending between the open end of the corresponding cavity and the open end of each other said cavity.

An embodiment of the invention will now' be described, by way of example, with reference to the accompanying diagrammatic drawings in which:

FIG. 1 shows a cutter for forming a post and a groove I FIG. 2 shows a perspective view of an array of glowdischarge cathodes and an anode frame in the relative positions they will occupy in a completed electrical glow-discharge display device; and

FIGS. 3(a) and 3 (b) show plan and cross-sectional views respectively of the components of FIG. 2 with a block of electrically insulating material 'moulded around them, the section of FIG. 3 (b) being taken on the line (b) (b) ofFIG. 3 (a).

In FIG. 2 an array of cathodes I together with supply leads 2 are formed from a sheet of a glasssealing alloy such as nickel-iron, chrome-iron or nickel-cobalt-iron by photo-etching are situated in an envelope 20 containing an ionizable gas. Parts 3 of the plate interconnecting the supply leads are left in situ for the moment in order to maintain the cathodes 1 in their correct positional relationship. Anode frame 4 is also made from a sheet of nickel-iron, chrome-iron or nickelcobalt-iron and a supply load 5 thereto is bent so that it terminates in the same plane as the leads 2.

In FIG. 3 a block 6 of electrically insulating material, for example that available under the Registered Trade Mark FUSITE K, has been moulded around the cathodes 1 and anode frame 4 so that the supply leads 2 and 5 project therefrom. The mould used is such that cavities 7 are formed in the top face of block 6, these cavities each terminating at anindividual cathode 1. To this end the surface of the mold corresponding to the top face of the block is provided with posts, on the tops of which rest the cathodes 1 during the moulding process. In addition the posts in the mould are surrounded by grooves with the result that a continuous ridge 8 is formed on the top face of the block 6 surrounding each cavity 7. Thus a continuous recess 9 surrounds each cavity 7.

In a practical embodiment the cavities 7 were approximately 1 mm deep and the recesses 9 were approximately 0.25 mm deep. The ridges 8 were approximately 0.25 mm wide and the cavity diameters were approximately 1 mm. The cavity spacing was approximately 2 mm between centers and the plane of the anode frame 4 was approximately 0.25 mm from the open ends of the cavities 7, i.e. from the peaks of the ridges 8.

The assembly of FIG. 3 also includes an additional cathode 10 situated at the bottom of a cavity 11 in the block 6. This is to serve as a full stop or decimal point in the display and, because it is a considerable distance from the cavities 7, it is not necessary to provide a recess around the cavity 11 (although of course such a recess may be provided if desired). An exhaust tube 12 terminates in a hole 13 opening into the upper surface of the block 6.

A substantially flat anode (not shown) made for example by photo-etching or by mechanically expanding a metal plate of, for example, the material available under the Registered Trade Mark KOVAR until it assumed a mesh-like structure, was then welded to the anode frame 4 so that it was supported thereby. A clear or translucent viewing window plate (not shown), made for example of the material available under the Registered Trade mark KODIAL was then sealed all round to the surface 16 of the block 6 by means of a solder glass. The metal portions 3 interconnecting the cathodes were removed.

, The device was then evacuated through the tube 12 and filled with pure neon or a neon argon mixture at a total pressure in the range 50-200 Torr.

The completed device was then aged by applying an operating potential of at least 280 Volts between each cathode and the anode, and continuing this application until sputtering from the cathodes due to the resulting electrical discharge caused an appreciable amount of cathode material to be deposited on the cavity walls, so

that this material formed a good electrical contact with the cathodes proper. A considerable reduction in striking and maintaining potentials occurs during this process.

The dimensions and relative locations of the cathodes and anode and the gas composition and pressure were such that the application of ZOO-230V between each cathode and the anode resulted in the generation of negative-glow optical radiation in the resultant glow-discharge, the positive column part of the discharge being substantially or completely suppressed.

Although circular cavities 7 and ridges 8 have been illustrated it will be appreciated that other shapes, e.g.

square, are also possible.

It will also be appreciated that, although electrically separate cathodes l have been shown, it is alternatively possible to make the device suitable for cross-bar addressing. To this end the cathodes in each row or column may be electrically connected together and the anode may be replaced by a number of anode strips each for co-operating with a column or row of cathodes respectively. If this is done the anodes may conveniently be formed by conductive strips of, e.g. tin oxide, deposited on the inner surface of the window. The cathode array may then be made up of a number of parallel strips orthogonal to the anode strips. A glow discharge display device incorporating these features is described in British Patent Specification 1, 153,674.

What we claim is:

1. An electrical glow-discharge display device comprising an envelope containing an ionizable gas, said envelope comprising a viewing window and a block of electrically insulating material sealed to said window,

said block having an array of cavities in the face proximate to said viewing window, a glow-discharge cathode positioned at the base of each cavity, and at least one anode facing and spaced from the open ends of said cavities for co-operating with said cathodes to define an array of individually addressable glow-discharge paths through the gas, the open end of each cavity being completely surrounded by a separate ridge and recessed portions of the block separating the ridges from each other.

2 device as claimed in claim 1, wherein the cathodes are integral with said block.

3. A device as claimed in claim 1, wherein a ridge is provided around the circumference of said block face, to which ridge is sealed said viewing window. 

1. An electrical glow-discharge display device comprising an envelope containing an ionizable gas, said envelope comprising a viewing window and a block of electrically insulating material sealed to said window, said block having an array of cavities in the face proximate to said viewing window, a glow-discharge cathode positioned at the base of each cavity, and at least one anode facing and spaced from the open ends of said cavities for co-operating with said cathodes to define an array of individually addressable glow-discharge paths through the gas, the open end of each cavity being completely surrounded by a separate ridge and recessed portions of the block separating the ridges from each other.
 2. A device as claimed in claim 1, wherein the cathodes are integral with said block.
 3. A device as claimed in claim 1, wherein a ridge is provided around the circumference of said block face, to which ridge is sealed said viewing window. 